Windows XP running slow during download or installation.

I just installed Windows XP and i have been getting this problem. I have a fresh install of windows XP. I have checked for spyware and viruses just incase. I have checked my running processes and there are no unusual processes running. I have a good computer. Intel Core Duo 2.4ghz, I have 4gbs of ram. I have no clue what is going on. ArmA took an hour to install. Whenever i download or install something windows will just lag. My mouse cursor lags horribly. I previously had vista and i had windows xp before that and they worked fine. Only reason i uninstalled vista is because some of the stuff i use and play don't work properly. Anyone know what the problem may be?

Yes. I believe that xp does not support more than 3gbs. I know there is a way to make it recognize all 4 gbs but i don't think it uses more than 3gbs. I had Windows XP Pro when i have had 4gbs and i did not have this problem. All i can think of is it may be my Hard Drive maybe i somehow broke it by reformating it? i don't know. It appears that whenever my computer writes to my harddrive windows will start to slow down. My hard drive is far from being full on space so i am not sure what is going on.